Can I use my competitor's trademark in my product description?

You are referring to nominative fair use. To enjoy that statutory (15 U.S.C. s 1125(c)(3)(A)(i)) exemption to infringement, at a minimum you will want to be sure to use as little of the mark(s) as possible (e.g., just the word mark FACEBOOK, not any associated logos), use the mark(s) in a narrative fashion and not as a brand identifier (e.g., "...unlike Facebook, we utilzie XYZ to do XYZ..."), and add disclaimers everywhere that you are not at all associated with Facebook and that FACEBOOK is a registered trademark of Facebook Inc., etc. Lastly, and most importantly, be sure to show any proposed advertising material to your IP counsel prior to publishing it.